I could use help with my first 18 civ custom prince game

[Alpha90]

This is the first time posting on this site and I am a new member but I have been reading the board for quite awhile.

I am currently running a custom prince game and my first game with 18 civilizations. my game is marathon speed with a huge map and the only customization I have made are that each civilization requires a complete kill, the only victory condition is to capture and kill all of the other civilizations, and I modified my XML file to remove any possibilities of global warming.
My game has gone seemingly well but I have come to a major dilemma that leads to a fork in the road that I cannot seem find my way out of. My civilization is at a point where a war is inevitable. I am not the leader in technology by any means but I have traded enough to be a military contender for a possible defensive role but I have zero striking power against my long time rival pacal. Which will lead me back to my fork do I finish the Manhattan project or do I go nuke free?
I have played both eventualities first going with a nuclear war. I have enough time before Pacal invades or enough time for my preemptive strike to build many nuclear bombs and level pacal’s productive countryside his main resource and cities but not enough to withstand a sustained war. Choosing this path I can take a few now radioactive cities and land that was once his heartland (with ecology far far away) but still being too small in size I can’t sustain a ground war.
With that choice I played my Civ for another 100 years till the mid 2020’s (this point in time was 1887) with massive political fallout from my nuclear war 1 of my games superpowers and vassal chain master hates me for nuking his friend and the other is my ally but cannot hold a defensive pact for very long because he keeps going to war.
After years of prosperity and troop growth I am still no match for 6 civilizations so I stay out of wars with my new found enemies until the Ethiopia the super power that hates me open a war with an all out nuclear attack against me and his vassals follow suit and my Civ is reduced to nothing.
Going back to my original fork in the road If I don’t build nukes and just concentrate on infantry Pacal will overrun my Civ with 3 or 4 Stacks of doom made up of anti tank , Calvary, and about 10 artillery each.
I just do not know what to do. Is my game winnable at all. I am attaching the save that i keep refering back to.

 

[coanda]

Yes, it's winnable. The modern age is full of options and tricks for an intelligent human to take advantage of.

Here's some stuff to keep in mind:
1. Espionage can be quite powerful at this point in the game. Note that the only reason Zara likes Pacal is because they're both running Theocracy. If you use spies to force either of them to switch out of that, suddenly Zara doesn't like Pacal any more. That means you can happily nuke away at Pacal without any diplomatic penalties.
2. Remember to ask for 10 gold from Zara the turn before you declare war on Pacal - if he goes along with it, he is incapable of declaring war on you for the next 10 turns (maybe 30 on marathon? I don't know). That's a nice long window for a modern-age war; by the time that wears off you should have won already, so you don't need to worry as much about dogpiling.
3. Take advantage of open borders agreements. Base airplanes in other civ's cities from which to run recon missions in advance to help plan your attack. Rebase tactical nukes and airlift tanks into other civ's cities if they provide a better line of attack at a target.
4. Nuclear war is all about planning and preparation. If he'll give you time to prep it, you could take 22 cities on your first turn of war with him (it'd take about 3 tactical nukes and 3 tanks per city, plus 3 subs and a transport for ones you need to hit from the coast) - leaving him plus Justin with a total of only 8 cities. You could totally eliminate Justin on turn 2, and totally eliminate Zara within 5 turns (possibly 4).
5. If you aren't going nuclear, the modern age war is about air superiority. If you control the skies, you will win.
6. Trading can be very effective late in the game. For example, I notice that you could easily pick up 5-6 health per city just from trades with other civs (Asoka wants your oil and will offer Bananas + 8 gpt for it; Joao will trade sheep + cows for iron, gems, and 9 gpt).
7. Don't be afraid to settle "filler" cities. You've got a lot of very juicy flat grassland just sitting there; if you build a city or two there, you could probably get that up to a contributing city fairly quickly.
8. Think about your civics. The last civics are not necessarily the best (in fact, Environmentalism is on average a little weaker than State Property and Free Market). In your particular situation, I'd likely be in Police State and State Property, and possibly in Nationhood and/or Theocracy. If you switch to State Property, you want to get your workers busy replacing a lot of those towns and villages with workshops - it'll greatly increase your production, which is far more important at this point in the game than commerce.
9. Don't be afraid to stop teching. Once you've got the techs you need to win, feel free to shut off your research and focus it into espionage or wealth if that will help you more.

Were I you, here's what I'd do:
Use the great artist to key up a Golden Age. Switch civics to Police State and State Property. Build some more workers, and get them all working replacing towns with workshops. Tech straight to radio. Build subs in coastal cities, build tactical nukes everywhere else. Build a road to hook up your aluminum! Build subs, tactical nukes, transports, tanks, and infantry. Move them into position (remember, tac. nukes in groups of 3). Keep a good eye on Pacal to try and anticipate when he's planning to strike and preempt him with your own attack. Use spies to switch Zara to Free Religion before declaring war or launching any nukes. Make sure to nuke Pacal's SoD's on turn-1 so he can't use them against you. Go crazy, try to wipe him out ASAP. Take your expanded worker core you built earlier and slap down workshops in all these new cities you just took to get them running faster, and start prepping for war 2. From that point on, it should be fairly easy to win (a little judicious work on diplomacy can keep Zara from declaring on you until you're ready to backstab him, and once you control your entire continent there's no way you're losing). If Pacal doesn't play along and declares war before you're ready, you've got to have a small force in place to take a few cities from him quickly and kill his initial SoD... then you just peace with him on any terms he'll accept as soon as he's willing to talk, and go back to prepping for an actual war.

 

[revengeofmakno]

Good suggestions from Coanda.
I am not as keen on using nukes but the tactics he describes for them can be very effective.

I'd re-empahisize air power. I've never lost a fight when I had control of the air even when the opponent had MUCH larger numbers of ground troops. It's even better on the defense than than offense. Those stacks based on artillery will have to crawl through your cultural area while you weaken them every turn with bombers. As they weaken, you can hit and run using your road network especially if you have tanks or mech infantry. Another tactic is to have an entrenched hill or forest in the path of the stack that is being bombed. The AI will likely attack it anyway and grind away a lot of the weakened troops. Machine guns are good in that role. Even very large stacks can melt away quickly under those circumstances.
If you concentrate and take down a big stack, the opponent is often willing to make a truce and if not after one stack is down, then after the second one almost certainly. You can then use that peace to build up to what you need or, if the situation is positive, forget peace and go over to the attack.